1. Field of the Invention
The present invention relates to a control system for controlling the timing for making an electric spark in the engine of a vehicle.
2. Description of Related Art
There is the increasing tendency that engines, particularly engines for automobiles, are designed to retard the timing for sparking when the knocking of the engine is sensed by a knocking sensor.
Control of the ignition timing by using the knocking sensor is not sufficient to fully prevent the knocking because the control is implemented after the knocking has occurred. Hence, it has been proposed that the ignition timing be retarded in a predetermined amount in anticipation when a running state is sensed in which the knocking is likely to occur. Japanese Patent Unexamined Publication (Kokai) No. 138,164/1988 discloses the technique in which the ignition timing is retarded in a predetermined amount in advance at the time of acceleration when the knocking may readily occur. And an amount of retarding the ignition timing is set to become largest at the time when acceleration is detected and to be decreased gradually to a smaller magnitude.
For conventional systems in which the amount of retarding the spark timing is set so as to become gradually smaller from the time when acceleration is detected, hesitation or a delay of causing acceleration may be likely to occur at the initial time of acceleration. This phenomenon has been found to occur because the amount of retarding the spark timing is apt to be excessive at the initial time of acceleration. More specifically, as acceleration is detected, for example, by checking a variation in accelerator opening angles or a variation in amounts of intake air, the amount of intake air within the combustion chamber, i.e., a combustion pressure, may be increased with some delay in response. In other words, it can be said that the knocking is most likely to occur at a cylinder which is to be sparked after a few cylinders from the time when acceleration is detected. This means that the spark timing is retarded to an excessive extent at the cylinder to be sparked immediately before the cylinder which is most likely to cause knocking, so that the hesitation may occur as a result of this retarding in an excessive amount.